Test that function returns correct value

In a file named history.js I want to test that {getMarketLabel(sel.get('market'))} returns the correct/expected value from a test. I am using skin-deep testing so far I only have the following:

  it('should ...', () => {
    expect(getMarketLabel)
  }

The getMarketLabel function takes a string in the test the string can be defined as foo it should then return the same string back (foo) this is what I want to test. I want to test that this has been called and returns said string.